This project addresses the antigenic specificities of the human target cell determinants which can be identified in the in vitro cell mediated lympholysis (CML) assay. The relative strength of the HLA-A,B and C determinants as targets for the cytotoxic T-lymphocytes is studied by effector cells which are generated in families against HLA-haplotypes with strong positive genetic linkage disequilibrium. This method is also used to identify new CML target determinants which at present cannot be detected by serological methods. The study has so far succeeded in identifying a set of new CML target determinants which are coded for by genes linked to HLA.